The present invention relates to a guide rail apparatus and, more particularly, to a guide rail apparatus for guiding an object around the portion of piping having complicated form such as elbow or the like. The guide rail apparatus of the invention can be applied, for example, to the guiding of running type ultrasonic flaw detector for examining weld parts of piping in unclear power station.
In plants such as nuclear power station, it is necessary to effect a periodic check of weld parts of the pressure vessel, piping and so forth for any leakage. Non-destructive inspection, particularly the ultrasonic flaw detection, is the most popular way for examining the weld parts. Hitherto, the ultrasonic flaw detection has been made mainly through manual work. Recently, however, it has been proposed to automatically and remotely control the scanning probe in order to achieve a higher efficiency. In such a method, the driving apparatus for driving the scanning probe is guided along a guide rail apparatus in the form of links previously arranged around the piping, in order to obtain correct information concerning the position of the probe. Most of the guide rail apparatus heretofore proposed, however, are designed for straight portions of the piping and, hence, can be applied only to several tens of percents of the whole portion of the piping. Namely, the weld parts of piping in nuclear power station are found mainly in the following portions; the portion where the axis is flexed, portion where the diameter of the pipe is varied, portion where an equipment is connected, and the portion where the pipe is branched or dispersed. In every part of a piping system there are portions where the axis is flexed or bent. Therefore, the rate of application of the automatic scanning system can be increased considerably by designing the guide rail apparatus for application to complicated portions of piping such as elbow.
As shown in FIG. 1, in a conventional probe driving apparatus for straight portion of the piping, a split-ring type guide rail 1 embraces the straight portion 2 of a piping in such a manner that the circumferential line of the guide rail 1 extends in parallel with the weld line 3. A driving unit 4 is mounted on the guide rail 1 by engaging rollers 5 to be able to run along the guide rail 1 in the circumferential direction so that the probe 6 scans the pipe around the weld line 3 in both circumferential and axial directions. The probe 6 is resiliently pressed against the surface to be examined by a holder 7 through a spring 8. An arm 9 carrying the holder 7 extends to the opposite side of the driving unit 4 and carries at its other end another holder 7 which presses a ball 10 resiliently against the pipe surface through another spring 8, so that the reactional force is exerted to press the probe 6 against the pipe surface due to a lever action of the arm 9. FIG. 2 shows another conventional apparatus in which a guide rail 1 is attached to the outer surface of an elbow 11 for permitting the probe 6 to scan the portion in the vicinity of the weld line 3, wherein the axial length is varied in accordance with the movement of the guide rail 1. In this known apparatus, it is necessary to vary the angle between the guide rail 1 and the arm 9 around the axis 14 of rotation and also to vary the angle between the examined surface and the arm 9. For these reasons, various difficulties are caused such as complicated manipulation, uneasy handling and troublesome processing of signals for detecting the position of the probe 6.
In Japanese Patent Application No. 92939/1978, a probe driving apparatus for an ultrasonic flaw detection of piping is proposed. However this proposed driving apparatus, however, is intended for straight pipes and operates in a manner explained hereinbelow with reference to FIG. 17. A driving unit 203 is attached to a track 207 secured to a straight pipe 201 by openable rollers 206. The driving unit 203 incorporates a motor the power of which is transmitted to a pinion 205 meshing with racks 208 formed on the track 207 so that the driving unit as a whole moves in the circumferential direction. At the same time, another motor drives a screw (not shown) extending in parallel with an arm 204 so that a holder 211, incorporating a nut meshing with the screw, is moved accompanying the arm 204. The scanning probe 202 for transmitting/receiving ultrasonic wave is made to run in both of circumferential and axial directions to thereby automatically conduct the examination. The scanning instruction is given from a remote plate by means of a cable. This apparatus, however, cannot be applied to the pipe of complicated form such as an elbow 210, because the length of the arm 204 is too large and abuts the pipe surface and because the probe 202 cannot delicately follow the examined surface of complicated form. Thus, this apparatus also fails to improve the rate of application of automatic ultrasonic flaw detection to the inspection of piping.